The stakes are considerable. The Antarctic Ice Sheet as a whole holds the equivalent of 57.9 metres of global sea level rise, and the East Antarctic Ice Sheet alone accounts for 52.2 metres of that total, an order of magnitude more than its western counterpart. While West Antarctica has dominated headlines with losses concentrated around Pine Island and Thwaites glaciers, Wilkes Land has quietly emerged as the region of East Antarctica losing the most mass. Previous work identified Frost and Holmes glaciers, both of which drain into Porpoise Bay, as among the top contributors to cumulative ice loss in East Antarctica between 1979 and 2017, behind only Totten and Denman glaciers. Yet despite this signal, the glaciers of Porpoise Bay had never been examined in the detail that their importance demands.

Weatherley and her colleagues set out to close that gap by measuring four key parameters across four outlet glaciers: Frost, Holmes East, Holmes West, and a smaller flow feature the team calls Glacier 1. They mapped the position of the ice-shelf calving fronts using imagery from Landsat, ASTER and Sentinel satellites, extending the record back to 1963 with declassified ARGON photography. They tracked ice surface elevation using multiple satellite altimetry datasets, measured ice velocity from the ITS_LIVE product, and located the grounding lines, the critical boundary where grounded ice begins to float, using differential synthetic aperture radar interferometry, or DInSAR, supplemented by a neural network trained to delineate grounding lines automatically from interferograms.

The results reveal a pattern of change that is hard to dismiss as noise. Frost Glacier’s grounding line retreated 17.17 kilometres between 1996 and 2014, an average rate of roughly 0.95 kilometres per year, with the fastest retreat, more than two kilometres per year, occurring between 1996 and 2004. Holmes East Glacier retreated up to 15.24 kilometres in just five years at the start of that period. If the estimates hold, Frost would rank among the fastest-retreating glaciers in East Antarctica on decadal timescales, with rates comparable to those recorded at Thwaites and Pine Island glaciers in West Antarctica. The authors are careful to flag substantial uncertainties, since the comparison combines datasets that delineate different parts of the grounding zone using different methods, but the retreat is broadly consistent with independent estimates from other studies.

The thinning signal is equally striking. Between 2003 and 2017, the grounded ice at Holmes West Glacier lowered at an average rate of up to 1.22 metres per year at the grounding line, a figure that places it among the most rapidly thinning glaciers in East Antarctica, rivalled in the published record only by Totten Glacier. The thinning propagated inland, reaching 0.34 metres per year ten kilometres up-ice, a spatial pattern characteristic of dynamic thinning driven by changes at the coast rather than by shifts in local snowfall. Because no long-term trends in precipitation or firn densification have been reported for the region, the researchers attribute the elevation loss to the ice itself flowing faster and drawing down its surface, a hallmark of dynamically forced mass loss.

What is driving these changes? The evidence points firmly toward the ocean. Warm, salty modified Circumpolar Deep Water, or mCDW, was detected at the continental shelf break near Porpoise Bay through measurements collected by instrumented seals from the MEOP consortium and by Argo profiling floats between 2004 and 2021. The water masses observed there, with temperatures above freezing at depth and salinities exceeding 34.5 grams per kilogram, match the signature of mCDW in East Antarctica. Reanalysis data from the EN4 dataset further suggest that water warmer than zero degrees Celsius has been present below roughly 450 metres depth on the continental shelf since at least the 1990s. Crucially, gravity-derived bathymetry reveals deep sub-ice-shelf cavities, between 650 and 750 metres deep and deepening inland, beneath Frost, Holmes East and Holmes West glaciers, providing plausible pathways for this warm water to reach the ice from below.

The melt rates implied by this oceanic heat delivery are extraordinary. Previous work calculated an average basal melt rate of 13.3 metres per year beneath the Holmes Ice Shelf between 1994 and 2018, the highest of any ice shelf in East Antarctica and fourth highest in all of Antarctica, exceeding even the melt rate beneath the Totten Ice Shelf. The ice shelf has also been thinning at its surface, with satellite altimetry recording losses of up to 3.07 metres per year on the floating ice, and pinning-point analysis suggests the thinning began at least fifty years ago. The picture that emerges is one of warm water circulating beneath the ice, melting it from below, thinning the floating tongues, reducing their buttressing effect, and allowing the grounded glaciers upstream to accelerate, thin and retreat.

The study also documents a striking rhythm of calving. The ice shelves of Porpoise Bay underwent near-synchronous calving events in 2006 to 2008, again in 2016 to 2017, and in a previously unidentified episode in 2021 to 2022, each time advancing back to within about a kilometre of their previous maximum extent before calving again. The team found that these events coincided with unusually low sea-ice concentrations in the preceding winter and spring, and with the break-up of the iceberg mélange, the jumble of sea ice and icebergs that presses against the ice front. Sea ice and mélange exert a resistive backstress on calving fronts, and their removal has been linked to ice-shelf breakup elsewhere in Antarctica. Because calving events at Porpoise Bay removed more than the roughly 18 percent of ice-shelf area that modelling identifies as dynamically passive, the losses translated into measurable speed-ups of the glaciers behind them, with velocity increases of several percent following the largest events.

Perhaps the most consequential finding concerns Holmes West Glacier. Its grounding line currently rests on a local bedrock high that appears to have shielded it from the full force of the warm water, which may explain its comparatively modest retreat rate of around 70 metres per year. But that pinning point sits at the very edge of a steep retrograde bed. Within two kilometres of inland retreat, the bed drops by 650 to 700 metres, and different bathymetric datasets suggest the reverse slope may continue for 25 to 35 kilometres inland. If the glacier unpins from its bedrock high, which the authors suggest could happen within a decade at current retreat rates, warm water would gain access to deep grounded ice, potentially initiating marine ice sheet instability, the same self-reinforcing retreat mechanism feared at Thwaites Glacier. The Holmes catchment holds the equivalent of roughly 11 centimetres of global sea level rise, and an adjacent ice rise that currently buttresses the flow could also lose its grip.

The authors emphasise that urgent improvements to bed elevation data are needed before the region’s future can be modelled with confidence, since the bathymetric uncertainties in this poorly surveyed corner of Antarctica are large enough to change the prognosis entirely. Nevertheless, the convergence of evidence, thinning that propagates inland, grounding lines retreating across retrograde slopes, modest but persistent flow acceleration, warm water at the shelf break, and deep cavities connecting ocean to ice, paints a coherent picture of a region responding to oceanic forcing. As Antarctic sea ice enters an era of record lows and increasing anomaly persistence, the stabilising seasonal blanket that has repeatedly broken and reformed over Porpoise Bay may grow thinner and less reliable. What happens next at these unassuming glaciers could help determine how much of East Antarctica’s enormous ice reservoir stays put in a warming world.

Subject of Research: Ocean-driven dynamic thinning and grounding line retreat at outlet glaciers in Porpoise Bay, Wilkes Land, East Antarctica

Article Title: Dynamic thinning and grounding line retreat in Porpoise Bay, Wilkes Land, East Antarctica

Article References: Weatherley, M., Stokes, C. R., Jamieson, S. S. R., Ramanath, S., & Silvano, A. (2026). Dynamic thinning and grounding line retreat in Porpoise Bay, Wilkes Land, East Antarctica. The Cryosphere, 20(9), 5509-5532. https://doi.org/10.5194/tc-20-5509-2026

Image Credits: AI Generated

DOI: 10.5194/tc-20-5509-2026

Keywords: East Antarctic Ice Sheet, Porpoise Bay, Wilkes Land, grounding line retreat, dynamic thinning, Circumpolar Deep Water, ice shelf calving, sea ice, marine ice sheet instability, Aurora Subglacial Basin, satellite remote sensing, sea level rise

The basin’s vulnerability stems from its bathymetry. Much of the bedrock beneath the Wilkes Subglacial Basin sits below sea level and deepens inland, a configuration known as a retrograde bed slope. That geometry is the essential ingredient for what glaciologists call marine ice-sheet instability. When the grounding line, the boundary where grounded ice begins to float, retreats onto such a slope, the ice at the grounding line becomes progressively thicker, increasing the outward flux of ice and driving further retreat. The result is a positive feedback that can continue even if the climate forcing that triggered it stabilises. Classic theoretical work on grounding-line dynamics, notably the stability analysis published by Christian Schoof in 2007, formalised this behaviour, and the Wilkes Subglacial Basin is now recognised as one of the largest marine-grounded basins in East Antarctica where the feedback could operate at scale.

The review’s synthesis of palaeoclimate evidence is perhaps its most striking element. Marine sediment cores recovered from the continental shelf offshore Wilkes Land, together with ice-sheet model simulations, indicate that substantial retreat of the basin’s ice occurred during past warm periods, most notably during the Pliocene epoch roughly three to five million years ago, when atmospheric carbon dioxide concentrations were comparable to today’s. Geochemical proxies in deep-sea sediments record deglacial events with clear biogeochemical responses downstream of the basin, and iceberg-rafted debris in Southern Ocean sediments testifies to episodes of enhanced ice discharge. Model reconstructions of specific Pleistocene interglacials, including Marine Isotope Stages 31, 11 and 5e, suggest repeated episodes of ice loss from the basin, although the review is careful to note that the precise temperature thresholds at which such retreat was triggered remain uncertain.

That uncertainty matters because it bears directly on the question of commitment. If the basin retreated substantially during interglacials only modestly warmer than the pre-industrial climate, then the margin of safety under current warming trajectories may be thin. Recent analyses of Pliocene sea level, drawing on geographically diverse geological archives, imply global mean sea levels several metres above present during that epoch, and the Wilkes Subglacial Basin is one of the few sectors of East Antarctica with sufficient ice volume to account for a meaningful share of that rise. The review’s authors, an international team led by Matt King of the University of Tasmania and including specialists spanning glaciology, oceanography, geophysics and palaeoceanography, argue that reconciling sedimentary archives with model simulations is essential to pin down how much warming the basin can absorb before retreat becomes self-sustaining.

Observations of the present-day ice sheet add a further layer of concern. Satellite altimetry, gravimetry and interferometric synthetic aperture radar measurements reveal multidecadal retreat of the grounding line in parts of the Wilkes Land sector, along with thinning and, in places, collapse of key fringing ice shelves. The Cook Ice Shelf and the Ninnis and Mertz glacier systems, which drain large portions of the basin, have shown measurable change, including velocity increases at Cook Glacier linked to ice-shelf loss and a documented subglacial flood event. Intriguingly, the review highlights that this retreat has not yet been accompanied by clear upstream surface lowering across the basin interior, leaving the ultimate cause of the observed changes unattributed. Whether the signal reflects ocean-driven melt at the ice front, atmospheric variability, or internal ice-sheet dynamics remains an open and pressing question.

The oceanographic context is shifting in ways that favour further change. Relatively warm, salty circumpolar deep water, which can melt ice shelves from below, has been shifting poleward in the Australian-Antarctic sector, increasing the risk of warm-water intrusions onto the continental shelf through the deep glacial troughs that dissect the Wilkes Land margin. At the same time, meltwater from Antarctic ice shelves is freshening the surface ocean, suppressing the formation of dense Antarctic bottom water that drives global deep-ocean circulation. Recent studies have documented reduced abyssal overturning and ventilation in the Australian-Antarctic Basin, and modelling suggests that sustained Antarctic meltwater release could slow the abyssal ocean’s overturning circulation within decades. A major retreat of the Wilkes Subglacial Basin would amplify this meltwater flux, with consequences that ripple through ocean circulation, carbon cycling and marine ecosystems far beyond the Southern Ocean.

Projections of the basin’s future under different emissions scenarios reveal the potential speed of change. Ice-sheet model simulations indicate that, once the grounding line retreats beyond key bedrock pinning points, retreat rates of up to roughly one kilometre per year are possible, an extraordinary pace for a continental ice sheet. The timing of such events is deeply uncertain, but the review stresses a more troubling point: decisions taken this century, in effect the emissions pathway the world follows over the coming decades, may commit the basin to multimillennial change. Because the retreat feedback operates on timescales far longer than human political and economic planning horizons, the full sea-level consequences of near-term warming would unfold over centuries to millennia, locking in losses that later mitigation cannot reverse. Sea-level feedbacks, including the gravitational and solid-Earth responses to changing ice load, modulate but do not eliminate this risk.

The review also identifies the processes that remain poorly constrained and that dominate projection uncertainty. Subglacial hydrology is one: the basin sits atop thick sedimentary sequences, and groundwater systems beneath the ice can amplify sliding and mass loss through basal water feedbacks. Geothermal heat flux, which softens the ice base and feeds subglacial lakes and drainage networks, is poorly mapped across the region. The stability of fringing ice shelves, which buttress upstream flow, depends on basal melt rates, calving dynamics and the protective role of land-fast sea ice, all of which are changing. Surface melt and meltwater ponding, historically rare in East Antarctica, are becoming more sensitive to atmospheric warming, raising the possibility of hydrofracturing-driven ice-shelf disintegration analogous to events observed on the Antarctic Peninsula. Improving the representation of these processes in ice-sheet models, and grounding them in field observations, is central to narrowing the spread of sea-level projections.

The authors’ prescription is unambiguous: a coordinated, multinational and multiyear programme of fieldwork and modelling focused specifically on the Wilkes Subglacial Basin. Such a programme would combine airborne geophysics to refine bed topography and subglacial geology, seismic surveys to characterise sediment properties and mantle structure, oceanographic moorings to monitor warm-water intrusions onto the shelf, sediment coring to extend the palaeo-archive, and targeted ice-core records to constrain past ice extent. It would also feed directly into model intercomparison efforts such as ISMIP6 and its successors, which currently struggle to agree on the basin’s response to given levels of warming. The review notes that planning for such coordinated fieldwork is already under way through international scientific committees, but the scale of the challenge, in one of the most remote and logistically demanding environments on Earth, demands sustained investment across multiple national Antarctic programmes.

What emerges from the synthesis is a picture of an ice sheet sector that is neither doomed imminently nor safely stable, but poised in a state whose trajectory depends on choices made now. The Wilkes Subglacial Basin has retreated before under natural warmth, its fringing ice is already showing signs of stress, and the ocean around it is warming and freshening in ways that erode its natural defences. With three to four metres of potential sea-level rise at stake, alongside far-reaching consequences for ocean circulation and Southern Ocean ecosystems, the basin has moved from a scientific curiosity to a first-order question for climate policy. The review’s central message is that the window for reducing uncertainty through observation is open, but narrowing, and that understanding this sleeping giant of East Antarctica is no longer optional.

Subject of Research: Climate vulnerability and dynamic instability of the marine-based Wilkes Subglacial Basin Ice Sheet in East Antarctica

Article Title: Dynamic instability of the Wilkes Subglacial Basin Ice Sheet, East Antarctica

Article References: King, M. A., Bertler, N. A. N., Anandakrishnan, S., Barruol, G., Bentley, M. J., Crosta, X., Christoffersen, P., Colleoni, F., De Santis, L., Escutia, C., Etourneau, J., Evangelinos, D., Ferraccioli, F., Golledge, N. R., Harris, M., Heil, P., Hill, N. A., Hodgson-Johnston, I., Hofstede, C., … Zhao, C. (2026). Dynamic instability of the Wilkes Subglacial Basin Ice Sheet, East Antarctica. Nature Reviews Earth & Environment. https://doi.org/10.1038/s43017-026-00827-6

Image Credits: AI Generated

DOI: 10.1038/s43017-026-00827-6

Keywords: Wilkes Subglacial Basin, East Antarctic Ice Sheet, marine ice-sheet instability, sea-level rise, grounding line retreat, ice shelves, circumpolar deep water, Pliocene, palaeoclimate, ice-sheet modelling, Antarctic bottom water, subglacial hydrology